During the production of paper products, significant amounts of scrap material are accumulated. This waste product, also known as broke, is generated from recycled products, products that do not fall within manufacturer's specifications, or from excess remaining after completion of the finished product. Problems have been experienced in the past, however, in recycling the paper fibers contained in many types of broke. For instance, prior to using broke for making a commercial towel, wiper or other similar product, it is often necessary to treat the fiber source to chemically degrade unwanted chemical constituents that might adversely affect the quality of the recycled paper product. One notable example of a contaminant that must be removed from broke before it can be recycled is latex. Latex is used as a creping adhesive in many papermaking processes, and is typically applied at high levels to one surface (e.g., single re-creped (SRC)) or both surfaces (e.g., double re-creped (DRC)) of the paper product.
Historically, latex-containing broke is broken down and recycled using chemical treatments. The purpose of the chemical treatments is to aid in degrading the latex polymer so that the mechanical action of the pulper may degrade the paper into individual fibers suitable for recycle in other products. One such chemical treatment includes treating the broke with hypochlorite, chlorine, or hypochlorous acid, depending on reaction conditions in the hydrapulper, to chemically oxidize the latex and thus allow the paper to be further broken down by the shearing and mechanical action of the pulper. The disadvantages of this process include high costs, potential chloroform generation, loss of brightness on unbleached fiber, and increased potential for corrosion of the paper machine.
Another chemical process entails treatment of the fiber with caustic and high temperature to swell the latex structure so that the mechanical action of the hydrapulper can defiberize the sheet. Although this process may sometimes be effective on unbleached grades of fiber, the disadvantages of this procedure are the need for heating the pulpers and the handling of caustic treatments. Caustic treatments may also darken the fibers. Finally, a third chemical process for repulping latex-containing broke includes treating the broke with persulfate salts. As with the other chemical procedures, the treatment with persulfate salts possesses disadvantages such as the need to neutralize residual persulfate, the need for pH and temperature adjustment, and the high cost of chemicals.
Accordingly, a need exists for an improved method of recycling latex-containing broke without chemical treatments, particularly those containing high levels of latex.